During the operation of a marine diesel engine, the circulating lubricant generally becomes contaminated with water. The effective working life of the lubricant is limited by the accumulation of water, which, apart from altering the lubricant properties of the oil, may have a deleterious effect on the metal to be lubricated. Similar considerations arise with other uses of oils.
In order to determine whether the oil is suitable for further use or for regeneration or rejection, it is frequently necessary to know whether water is present in the oil in excess of a predetermined tolerated proportion. Such a proportion might be in the region of a few percent, e.g. 1 to 5 percent by weight of wet lubricant, but substantially higher water contents can be encountered. On the other hand, it may be desired to apply a more stringent standard, of a fraction of one percent.
Devices are known by means of which the water content of an oil can be determined. For instance, a measured amount of oil may be confined in a closed vessel incorporating a pressure gauge together with a substance which reacts with water to produce gas. The amount of water present in the oil is then determined according to the pressure rise shown on the gauge. The oil may also be contacted in a vessel with a water-reactive substance and a carrier. The amount of produced gas is then measured by means of a separate manometer U-tube equipped with another manometric liquid and connected to the vessel, measuring the internal pressure developed.